Doctors said Abe was "extremely weak" and needs to be hospitalized for at least 3 to 4 days, according to hospital official at a press conference.

The prime minister went to see doctors at Keio University Hospital for feeling sick and received physical checkup in the morning, one day after expressing his intention to resign.

At a press conference broadcasted live, Abe's doctor said the premier has been suffering from stomach irritations, pain, poor appetite and other duodenum-centered symptoms, for all of which fatigue and stress should be blamed.

The doctor said those symptoms began to bother Abe over a month ago, and the premier has lost about 5 kg in weight over the past few months. He added that the premier's daily life could be thrown into confusion if the functional disorder worsens.

The hospital is planning to concentrate on medicinal rehabilitation in Abe's case.

Abe went to hospital on advice of his private doctors, who concluded in recent days that the premier's fatigue has reached a peak and should undergo a thorough examination, Kyodo News reported, quoting Chief Cabinet Secretary Kaoru Yosano.

Shortly after Abe's announcement of resignation, Yosano said the prime minister made the decision out of health reason. However, Abe himself did not mention any physical problems on Wednesday's press conference.

Japanese media quoted sources as saying that the premier felt unwell with his stomach recently and has even received intravenous fluids in the past week.